The invention relates to a flange connection.
Elastomer-sealed flange connections for the simple, quick and tight connection of two pipe parts have been known for a long time and in the most diverse types and are utilized in particular in vacuum technology when setting up vacuum systems.
Such elastomer-sealed flange connections are standardized as small flange connections, denoted as ISO-KF flanges, and as bolted flange connections, for example denoted as ISO-K flanges, internationally via PNEUROP (www.pneurop.org) or ISO (www.iso.org) and are applied in the vacuum industry.
The main nominal dimensions in small flange connections are: DN 10/16/25/40/50 ISO-KF and the auxiliary nominal dimensions: DN 20/32 ISO-KF. The dimensions are defined according to DIN 28403 and also according to ISO 2861/I. The two pipe ends bear flanges with conical tightening faces onto which acts an annular detachable clamp. Between the flange faces is disposed a centering ring with an annular rubber-elastic seal. The pipe axes are thereby made to coincide, the rubber-elastic seal is stayed and its compression is limited when the clamp is bolted tight. The thickness of the centering ring determines the flange distance and is defined, for example, according to the current ISO standard as 3.9 mm. Clamps encompass the flange and can also be realized as multipart, chain-like flanges. When applying pressure the centering ring is advantageously provided in the outer region of the flange and the seal subsequently lies in the inner region and is pressed onto the centering ring through the inner pressure. In vacuum applications the centering ring lies in the inner region and the seal is stayed against the inner portion. Such a small flange connection is described for example in CH 448 638. A further description can be found in the publication “Theorie und Praxis der Vakuumtechnik” by Wutz-Adam-Walcher, Vieweg Verlag, Second Edition 1982 (ISBN 3-528-04884-0) page 475.
The main nominal dimensions according to the standard for bolted flange connections are DN 63 ISO-K/100/160/200/250/320/400/500/630 ISO-K. K denotes herein clamp flange for the detachable securement by means of bolted flanges, clamps or claws. The dimensions are defined according to DIN 28404 and also ISO 1609/3669. A description of such bolted flange connections can be found in “Theorie und Praxis der Vakuumtechnik” by Wutz-Adam-Walcher, Vieweg Verlag, Second Edition 1982 (ISBN 3-528-04884-0) pp. 476-477.
According to this standardization one differentiates between:    a) Configuration with so-called rigid flanges which are secured each at one of the pipe ends to be connected. These have a rigid hole reference circle which serves for receiving bolts with which an annular seal located between the two rigid flanges is pressed, as has previously already been described for the small flange connection.    b) Configuration with so-called clamp flanges. These have an encircling slot-like turned flange groove into which laterally boltable clamps are hooked and subsequently tightened. Such flanges are rotatable before tightening.    c) Configuration with so-called overthrow flanges. These are provided with a hole reference circle and are bolted against one another. Before the tightening the flanges are rotatable. For example a rigid flange (for example according to ISO-F or DIN 2501) and an overthrow flange can be combined.
The several models of flange types or the type of bolting-together according to a to c can, on demand, be combined with one another.
In these known flange connections several differently formed centering rings are required for receiving and positioning the elastomer seal. For small flange connections, for example, five different centering rings are required in order to be able to cover all important applications, such as for vacuum, high overpressure, different required materials depending on the aggressiveness of the medium in the pipe line, as well as transition centering rings if different nominal flange dimensions are to be connected.
When used in vacuum technology it is undesirable that in these known small flange connections and bolted connections, regions with voids are generated, which release uncontrollably trapped gases and hereby represent sources of virtual leaks. Such virtual leaks are primarily formed with the configuration of the often utilized inner centering ring. Such leaks lead to undesirable impurities and long pump-down times in the generation of the vacuum and are in practice very difficult to locate. Vacuum technology involves extremely pure process applications and such leakage sites are therefore dreaded. In vacuum process systems often a multiplicity of connection sites is necessary and it is extremely important to avoid such uncontrollable virtual leaks.